


Hellspawn and the Ashen Demon

by essen



Category: Fire Emblem: Fuukasetsugetsu | Fire Emblem: Three Houses
Genre: Alternate Universe, Alternate Universe - Twins, Gen, My Unit | Byleth Twins
Language: English
Status: In-Progress
Published: 2020-04-01
Updated: 2020-04-01
Packaged: 2021-02-23 02:10:22
Rating: Teen And Up Audiences
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 2,819
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/23437390
Author URL: https://archiveofourown.org/users/essen/pseuds/essen
Summary: Twin Byleths AUBeles turns her forced appointment as a professor of Garreg Mach into a chance to learn more about her family and legacy. Byleth always thought becoming a master swordsman and delving into the mysteries of magic with the girl in his head were enough for him, but he finds himself increasingly involved in his students' success. Beles and Byleth must give their all to secure the future they envision, because the Agarthans hate fun.
Comments: 1
Kudos: 4





	Hellspawn and the Ashen Demon

**Author's Note:**

> Thank you, atreecat and friends, for your help editing.

**Byleth: Fire Emblem and dragon girls**

Byleth dreamed, as he always did, of a green-haired girl. She sat upon a greenish gray stone throne at top of a hundred greenish gray stone steps. An eldritch light illuminated the throne and himself. Beyond the light was endless darkness. As the years passed he grew older, but she stayed the same. The girl first awoke when he was thirteen. She couldn’t remember her name, or anything about her past, but she knew so many things that Byleth didn’t know that it was impossible for her to be a figment of his imagination.

There was a 48.87% chance she would be awake. When she was asleep, he would rest in the darkness. It was lonely, but it was better than not dreaming at all. His sister and father didn’t understand- they thrived off chaos and commotion respectively.

Today the girl was awake. She wasted no time with pleasantries, which was always appreciated. “I noticed you perform Windsweep in battle for the first time. You might be a decent swordsman after all!”

“Just decent?” Sure he hadn’t mastered it yet, but some more recognition for three months of practice would be appreciated.

“Should I praise you for swinging a sword? Back and forth, back and forth, a hundred times a day. If I commend you for anything, it would be for not getting bored of practicing the same motion 9000 times.”

He had  _ not _ done the same motion 9000 times. Each time he improved upon the last, otherwise he would be committing the wrong movements to memory. Properly executed, Windsweep would allow him to hit any enemy with no chance of eating a counterattack. His sister didn’t have the same patience for incremental growth as him, but she had perseverance and that was enough.

The girl leaned back and laughed. “I don’t need a piece of metal to destroy my enemies, but I understand you mortals have such limited magical power. Very well, I suppose I can find some encouragement for you.” She leaned her head on her right hand, looking around as if she could find an answer in the darkness. “Yes… if you keep up this rate of progress I may yet be able to rest easy in your ability to keep us alive.”

Byleth folded his arms. Just what kind of foes did the girl think he would be facing? The sort of folks who resorted to banditry were ill-trained if trained at all.

Once he mastered Windsweep he could take his Swordmaster proficiency. As a Swordmaster he could lead his own mercenary troop, and wasn’t that a thought? The Ashen Demon Mercenary Troop. He could handle the fighting and management, but the networking for better contracts and negotiating with clients… he shuddered. Maybe when Beles started her own troop he could be her right-hand man. What would they call themselves? The Hellspawn and Ashen Demon Troop? Kind of unwieldy.

The girl continued. “Your swordsmanship is progressing, but when are you going to master Agnea’s Arrow? I can’t teach you anything until you understand at least enough Reason magic for that spell.”

Byleth rolled his eyes. Agnea’s Arrow was A ranked, the pinnacle of Reason magic, at least as hard as learning Windsweep. The problem was, he could swing his swords a hundred times a day. He could only cast his most complex spell, the C ranked Bolganone, five times a day. “Should I learn Ragnarok next?” It was the natural progression of his magical studies, the B ranked fire Reason spell. But Agnea’s Arrow was a light Reason spell. “Maybe I study Sagittae instead?”

The girl folded her arms. “The fact that you have to ask betrays your inexperience in the matter. Think, Byleth!”

Byleth wanted to consider the arithmetic differences between light and fire Reason spells, but he didn’t actually know any light Reason spells. He should get a book or tutor the next time the troop visited a city.

He did know a lightning-based Reason spell. Fire, Bolganone, and Thunder all had explosive structures with exponential growth, but Thunder was narrower. He had a vague notion that light Reason spells were circular. He might be able to practice making light without fire by cutting off the parts of the equations that related to heat? Maybe light spells were closely related to Faith magic and that’s why he was struggling? Beles wouldn’t know but he could bounce some ideas off her…

His thoughts were interrupted by a familiar cry in the darkness. Beles was in danger!

No, he corrected himself. It was just another nightmare.

Probably.

He stared into the darkness, shifting his balance from foot to foot. He tried to get his line of thought back, but he couldn’t stop thinking about his sister.

Beles was fine.

Probably.

The girl said, “I can tell your thoughts are no longer with me. Go on. I won’t keep you here.”

“Sorry.” He bowed his head.

“Get out of here already!” The girl waved him out of the dream.

Byleth opened his eyes to the gray fabric ceiling of his tent. He pulled himself out of his bedroll and into his overcoat. With his sword in hand, he softly stepped through camp to the women’s side. He nodded at the early morning watch and they nodded back. Business as usual. With the ease of experience, he methodically wriggled into Beles’ tent without shaking or rustling the tent.

Byleth knelt by Beles’ bedroll and started humming. A strange tune, one he didn’t remember anyone singing to him. He didn’t know the words, but he didn’t need them. Beles stopped thrashing. Byleth began the verse again and Beles’ face relaxed.

Footsteps approached the tent. Byleth’s head and sword snapped up at the intruder, but it was just Father.

Jeralt scratched the back of his head. “You can’t keep coddling Beles like that,” he said, but even Byleth knew that he didn’t mean it.

Byleth frowned. “The war dream.” Again. It was always the war dream. Vast armies clashing together, a hateful blood-thirsty man and a hateful blood-thirsty woman. Relentless stabbing, blood everywhere. In many ways he envied Beles, but this was not one of them. No wonder she was always sleep-deprived.

Jeralt made his consolations, but he clearly had some pressing business. “There’s a group of bandits trying to kill some noble kids. Get Beles ready for battle.”

“Yes, sir.” Byleth knew she was already awake—their father wasn’t trying to be loud but Beles would be a fool to sleep so soundly on the road. He gamely tapped her on the shoulder and dived out of the way, narrowly avoiding a half-hearted fist to the face. It still could’ve given him a bloody nose.

Jeralt barked out a short laugh before leaving.

Beles groggily glared at him. “Why am I up so early?”

“Bandits.”

She groaned. “Bandits need sleep, too. Why the hell are they up so early?”

“Nobles.”

“Of course it’s nobles. That’s where all the money is. What did they do, flash a bag of gold coins while paying for a bowl of soup?”

Byleth had no answer for that.

Beles reluctantly rolled out of her bedroll.

Byleth said, “I’ll meet you at the campfire,” and got out of there before Beles started stripping. Her usual attire already showed off more than he would ever want to see.

**Beles: Fire Emblem and bandits**

Beles cracked her fists before tugging on her iron gauntlets. Maybe she could get a pair of steel gauntlets with the money from this impromptu job. It wasn’t often that a noble had a job worth taking that didn’t make her feel slimy inside. Byleth could upgrade to steel, too. Or maybe he’d prefer to pick up a shield?

Byleth unsheathed his iron sword. “Isn’t it strange?”

“What’s strange?” Beles stretched her shoulders and back as they jogged to the battlefield.

“Bandits attacking kids.”

Yeah, yeah, bandits are people, too. “Dad calls everyone kids.” Beles had never gotten solid numbers out of the old man, but he wasn’t exactly hiding the fact that he was long-lived. The nobles were probably adolescents. “Take a massive ego and pump it full of raging hormones. Even the Goddess herself would punch a noble kid.”

“Oh.”

Then there was no time to talk as they fell upon bandits chasing three nobles in red, blue, and yellow capes. At least their clients were easy to tell apart.

Beles smirked as her opponents’ eyes were invariably drawn to her chest or abs. It would be the second to last thing they ever saw, followed only by a fist to their face as she caved their skulls in.

Byleth followed her closely, guarding her back and taking out just as many bandits on his way. They regrouped with the three noble kids. And they were kids. They looked a few years younger.

A girl, white hair and red cape, wielding an axe. A rare sight. Most girls preferred magic or ranged weapons. The girls who did fight in melee tended to use swords or lances to augment their range. At least it looked like she had the muscle to handle such an unwieldy weapon.

Two boys. The dark skinned boy with a bright yellow cape had a bow. The three of them should’ve discarded their capes while running away from the bandits. Clothing was much easier to replace than lives. At least the boy was wearing an arm guard. His fingers were callused and his bow was scratched so she was willing to believe he was practiced enough to be of use in battle.

The other boy was blond with a blue cape and a well-worn lance. Come to think of it, light-colored hair was almost as bad as the capes. The lance looked like it would break in ten more good hits. Why didn’t he have a better weapon? Surely he could afford it.

Beles didn’t get much information from the kids that she didn’t already know. Yeah, there were a lot of bandits trying to kill them. No, they didn’t know how many or where their backup was. Yes, they could fight. At least she got their names.

“Dimitri, you’re with me. Edelgard, you’re with Byleth. Claude, stick with me, but cover Byleth and Edelgard, too.” She paired Dimitri’s longer reach with her gauntlets and Edelgard’s shorter reach with Byleth’s sword. She wasn’t planning to split up with Byleth, but in case they had to, she wanted the nobles to have direction. “Dimitri, I want you to watch my back.”

“Got it.” Dimitri’s stance was a bit stiff, but he would live.

Byleth studied Edelgard and said, “Stay on my right.”

To Claude, Beles said, “Shoot at your own pace, but warn us if bandits appear.”

“I hear you loud and clear, Beles!” Claude’s stance was a bit too relaxed, but he, too, would live.

She would make sure of it.

Conscious thought faded to the background as she fell into a cycle of identifying enemies, closing the distance, and punching their faces in. She was, of course, always aware of where her allies were. As Dimitri got into the fight, his rigidity faded away into savagery. Claude got more and more tense, whipping his head around at every movement and noise. Edelgard fell into tunnel vision, only considering the enemy before her.

At one moment, Claude screamed, “Edelgard! MOVE!” When she turned to look however, Byleth was blasting a bandit with fur shoulder pauldrons with Fire. The fur went up in flames and the bandit ran off while desperately ripping his pauldrons off.

Beles considered the merits of fur pauldrons. They could be stylish, if cared for properly.

“No more bandits?” Claude lowered his bow but didn’t unstring it yet. “Edelgard, are you okay?”

Edelgard shivered. “Yes, thanks to Byleth.”

Beles turned to Byleth. “Hey By, do you think I’d look good with—”

“No.”

She glared at him. “I didn’t even—”

“No.”

“Hmph!” Whatever. Byleth was boring, always wearing his uniform even when they were in cities. 

The three nobles hurried to thank them, scraping to ingratiate themselves. Such amateur recruitment pitches. She promised nothing and made no rejections, avoiding any attempt at sounding out her allegiance. On the inside she crackled at their frustration. If it wasn’t for the fact that the three nobles were the  _ future three leaders of Fódlan _ she wouldn’t have considered their requests at all. Did the bandits have any idea they were trying to rob/kill the Crown Princess of the Adrestian Empire, the Crown Prince of the Holy Kingdom of Faerghus, and the heir of the sovereign duke of the Leicester Alliance?

Claude was the first to break. “Let’s get right to it. Where does your allegiance lie, Byleth? Or do you not have a preference like your sister?”

Byleth said, “I like Faerghus in the winter.” Weirdo. The harvest season was the best time of the year. The most food, the best food, and the cheapest food, all at once. 

Claude’s eyes widened. “I’ve heard people say summer in Faerghus is the perfect weather, but I bet even Dimitri doesn’t have anything nice to say about Faerghus winters.”

Dimitri said, “Faerghus isn’t all frozen wasteland, Claude. And I agree with you, Byleth, there’s nothing quite like the quiet of winter.”

Edelgard shook her head, “That’s awfully close-minded of you, Claude.”

“Well, excuse me, Princess.” Rather than looking offended, Claude’s eyes were gleaming.

Beles tuned out the political dick-measuring and cast her attention on the man talking with Dad. He was a jovial knight with a nice beard. Dad looked more exasperated than he had ever been with her. They seemed like past acquaintances, and anyone would have a looser tongue than Dad.

Byleth could handle the noble kids. He liked to think he was hopeless at currying favor, but he did just fine being himself. She had always been the one who had to put effort into getting people to like her.

She slipped away and sidled up to Dad and the knight. “Hey Dad, the nobles are safe.”

“That’s great to hear, but I’m not your dad,” the knight said. He turned to her and did a double-take. “Captain Jeralt! Is this your kid?”

Dad let out a mighty sigh. “Beles, this is Alois, a Knight of Seiros. Alois, this is my daughter Beles.”

Beles held out a hand. “You’re Alois Rangeld? Dad’s told me so much about you!”

That brought an even wider smile to his face. Alois had a solid grip and an enthusiastic handshake. “Really! Captain Jeralt, I had no idea you liked me enough to tell your daughter about me!”

“I’m not your captain anymore,” Dad grumbled. “I’m just a mercenary now.” Just a mercenary? Dad was the famous Blade Breaker, the strongest and most-storied mercenary in all of Fódlan! Before that he had been the longest serving Captain of the Knights of Seiros! Dad always made a big deal about living a quiet life, but he wasn’t fooling anyone except himself. 

“Lady Rhea never demoted you,” Alois said. “Besides, you’ll always be Captain Jeralt to me!”

Beles said, “You were Dad’s squire, right?”

“Yep! I was his right-hand man, or at least that’s how I thought of myself!”

“Is it true that one time Dad got so drunk he got into a fight with a tree?”

Alois had a deep belly laugh, the kind that shook the ground he stood on. “Absolutely! He wrestled with it for a good two hours then got fed up and kicked it clean in half.”

“That’s enough,” Dad said. “Don’t fill my kid’s head with nonsense.”

Beles pouted. “How can it be nonsense if it’s true?” She shared another laugh with Alois.

“I need a drink,” Dad grumbled. “Beles, get everyone on the road.”

“Yessir!” Beles saluted.

Alois said, “Don’t go anywhere just yet! Captain, I insist you return to the monastery with me!”

The monastery… Garreg Mach Monastery? The seat of the Church of Seiros’ power? She had always wanted to see the cathedral there, but anytime she asked Dad always said he’d left on bad terms. Whatever happened 20 years ago, she couldn’t believe it was so terrible that Dad could never return. “Dad, can we go? Please? Please?” She clasped her hands together and looked up at him with sparkling eyes. Byleth still refused to learn how to produce tears on command, but it was so, so useful.

Dad sighed harder than he’d ever sighed before.

“What’s troubling you, Captain? You aren’t about to run off again, are you?”

Beles and Alois looked expectantly at Dad.

Dad turned away. “Even I wouldn’t dare run from the Knight of Seiros.” Yes!

“Come now, Captain, it’s not like that!”

“Yeah, yeah. Off with you, Beles.”

She saluted again. Dad was only delaying the inevitable. She’d have plenty of chances to get stories out of Alois on the road.

**Author's Note:**

> Fun fact, my working title was "Trash Byleth Twins AU," but at some point I got serious about the story. 
> 
> Stats (for fun)  
> Byleth (Lv 24 Mercenary): Sword B+, Brawling D+, Reason B+, Faith D, Authority C+, Riding C  
> Beles (Lv 24 Mercenary): Sword C, Brawling B+, Reason D, Faith B, Authority B, Riding C  
> Jeralt (Lv 35 Paladin): Sword B, Lance A+, Brawling C, Bow C, Authority A, Riding A 
> 
> I just want to read a finished Byleth Twins AU. That said, I can't promise this will be finished, but I do want to at least get to the timeskip.  
> Pairings may or may not happen, but they would be as featured as they are in the main game.


End file.
